Do tube shields help dissipate tube heat or do they trap the heat? The reason I ask is I'm replacing some shot tube sockets on a 2 x EL84 franken-amp I built years ago. The tubes hang down and they've always run a little warm so I want to kill two birds with one stone: add support AND help dissipate heat. So: Shielded socket? or Retainer strap socket? What do you think?